1. Field of the Invention
The present invention relates to the field of medical devices. In particular, the present invention related to power supply systems for transcutaneous energy transfer (TET) devices. Even more particularly, the present invention relates to an improvement in TET devices which simplifies such devices and improves their energy transfer efficiency.
2. Description of the Related Art
A TET device is a device for providing electrical power to an implanted mechanical or electrical medical device, such as prosthetic hearts and ventricular assist devices, without having to breach the skin to lead conducting wires therethrough.
An example of a TET device is shown in U.S. Pat. No. 4,665,896 (LaForge et al) dated May 19, 1987. That patent shows a blood pump system powered by a TET device having an external primary winding and an implanted secondary winding. It is designed to be regulated to a precise degree, the power delivered to an implanted medical device. However, it is not concerned with power transfer efficiency across the skin.
U.S. Pat. No. 4,408,607 (Maurer) dated Oct. 11, 1983, on the other hand, describes a TET device which charges an implanted capacitor. Power is then drawn by a implanted medical device from the capacitor. Maurer does not require particularly efficient TET efficiency, it will be understood, because it utilizes TET technology to provide an induced voltage to charge a capacitor. An efficient capacitor is, under Maurer's proposal, much more crucial than efficient TET. Moreover, the Maurer patent relates to very small power levels-on the order of those obtainable with a fairly small implanted capacitor. With Maurer's parallel tuned circuit, Q will fall at high loads levels.
In U.S. Pat. No. 4,741,339 of May 3, 1988, Harrison et al describe a TET with improved coupling between internal and external inductive coils. The means for achieving such improved coupling proposed by Harrison includes a circuit electrically coupled to the primary coil, tuned to increase the quality factor of the primary transmitter circuit which includes the primary coil. Harrison, as well is concerned with very low power levels, and accordingly, does not have application to a system designed to provide a power source for an artificial heart.